The present invention relates to fungicidal two-component mixtures having an unexpectedly enhanced activity that are based on metalaxyl having an R-enantiomer content of more than 70% by weight, and to the use of those mixtures in the control and prevention of infestation by Oomycetes. The metalaxyl component is referred to as active ingredient I.
The mixing partner 11 is one of the following fungicides:
IIA) 4-[3-(4-chlorophenyl)-3-(3,4-dimethoxyphenyl)acryloyl]morpholine (xe2x80x9cdimethomorphxe2x80x9d) (The Pesticide Manual, 10th Ed., pages 351-2, 1994), or
IIB) 3-anilino-5-methyl-5-(4-phenoxyphenyl)-1,3-oxazolidine-2,4-dione (xe2x80x9cfamoxadonexe2x80x9d) (Brighton Crop Protection Conference, Pests and Diseases 1996, Vol. I, pages 21-26). It is also possible to use salts or metal complexes of compounds IIA or IIB, for example copper or manganese salts.
In the narrower sense, the invention relates to mixtures of pure metalaxyl having an R-enantiomer content of more than 85% by weight, especially more than 92% by weight, or more especially more than 95% by weight. The best results are achieved with pure R-enantiomer that is substantially free of S-enantiomer.
Metalaxyl is methyl N-(2,6-dimethylphenyl)-N-(methoxyacetyl)-DL-alaninate and has the structure 
It has an asymmetrical *C atom and can be separated into the enantiomers in conventional manner (GB-1 500 581). Since 1975 it has been known by experts in the field that the fungicidal action of the R-enantiomer far exceeds that of the S-enantiomer, and the R-enantiomer is in practice considered to form the true active principle. Commercial metalaxyl is available in the form of a racemate. A need to resolve the racemate, half of which consists of the desired R-enantiomer, has never arisen in the past for practical reasons.
Completely surprisingly, it has now been found that R-metalaxyl in pure form, or in a form concentrated to more than 70% in the racemate, in co-operation with one of the fungicidal partners IIA or IIB, achieves unexpectedly high enhanced effects, some of which exceed the effects of the racemate-based mixtures (for example mentioned in EP-280 348 or EP-393 911) by factors of up to 10. Factors that might have been expected, based on the R-enantiomer content of th e racemate being approximately 50%, would be 2 at most.
With this completely unexpected result, the present invention represents a very substantial enrichment of the art and a possibility of reducing the total rates of application of fungicides used in the control of Oomycetes on plants, thereby safeguarding the environ ment. The dramatically improved degradability of metalaxyl in the soil as soon as the R -enantiomer content exceeds 70% by weight is known from WO-96/01559.
In addition to the two-component mixture I:II, the present invention relates also to a method of controlling fungi which comprises treating a site, for example a plant, infested by or at risk of infestation by fungi with a) component I and b) the compound II in any order or simultaneously.
Favourable I:II mixing ratios of the two compounds are from 30:1 to 1:30, especially from 10:1 to 1:10, more especially from 10:1 to 1:5. In many cases, mixtures in which the mixing ratio of compound I to compound II is from 1:1 to 1:5 are advantageous.
The compound mixtures I+II according to the invention have very advantageous curative, preventive and systemic fungicidal properties for the protection of cultivated plants. With the compound mixtures of the invention it is possible to inhibit or destroy the microorganisms that occur on plants or parts of plants (the fruit, blossom, leaves, stems, tubers or roots) of various crops of useful plants, while the parts of plants that grow later are also protected from such microorganisms. This applies especially also to microorganisms that have developed reduced sensitivity to metalaxyl.
The mixtures of compounds I and II are usually used in the form of compositions. R-metalaxyl (I) and the compound II may be applied simultaneously or directly one after the other to the area or plant to be treated, if desired together with further carriers, surfactants or other application-promoting additives that are customary in formulation technology.
Suitable carriers and additives may be solid or liquid and are substances that are expedient in formulation technology, for example natural or regenerated mineral substances, solvents, dispersing agents, wetting agents, tackifiers, thickening agents, binders or fertilisers.
A preferred method of applying a compound mixture that comprises at least one each of the compounds I and II is application to the parts of the plant above the soil, especially the leaves (foliar application). The frequency and rate of application depend on the biological and climatic living conditions for the pathogen in question. The compounds may also penetrate the plant through the root system via the soil (systemic action) as a result of impregnation of the locus of the plant with a liquid preparation or by means of introduction of the compounds into the soil in solid form, for example in the form of granules (soil application).
The compounds of the combination are used in unmodified form or preferably together with the adjuvants conventionally employed in formulation technology and are accordingly formulated in known manner, for example, into emulsifiable concentrates, coatable pastes, directly sprayable or dilutable solutions, dilute emulsions, wettable powders, soluble powders, dusts or granules, or by encapsulation in substances, for example polymeric substances. As with the nature of the compositions, the methods of application, such as spraying, atomising, dusting, scattering, coating or pouring, are chosen in accordance with the intended objectives and the prevailing circumstances. Favourable rates of application of the compound mixture are generally from 50 g to 1800 g of active ingredient (a.i.) per hectare (ha), especially from 100 g to 1000 g a.i./ha.
The formulations are prepared in known manner, e.g. by intimately mixing and/or grinding the active ingredients with extenders, such as solvents, solid carriers and, where appropriate, surface-active compounds (surfactants).
The agrochemical compositions usually contain 0.1 to 99% by weight, especially 0.1 to 95% by weight of compounds of formulae I and II, 99.9 to 1% by weight, especially 99.9 to 5% by weight of a solid or liquid adjuvant, and 0 to 25% by weight, especially 0.1 to 25% by weight of a surfactant.
Whereas commercial products are preferably formulated as concentrates, the end user will normally employ dilute formulations.
Suitable target crops are especially potatoes, vines, hops, maize, sugar beet, tobacco, vegetables (tomatoes, paprika, lettuce etc.), and also bananas, rubber, lawn grasses and ornamental plants. Other plants endangered by downy mildew are known, inter alia, from the literature on metalaxyl.